Technical data

17
SERVICING REFRIGERATION COMPONENTS
Servicing must be done by a qualified refrigeration engineer.
WARNING: Before doing any work on the machine ensure that
the power is switched and locked off and that all isolators are
tagged. If a refrigerant circuit is opened, it must be evacuated,
and recharged, after ensuring that the refrigerant is clean and
free from impurities, the filter-drier has been changed and the
unit has been tested for leaks. Before any operation on a refrig-
erant circuit, it is necessary to remove the complete charge of
refrigerant from the unit with a refrigerant charge recovery group.
General maintenance
• Keep the unit itself and the space around it clean and free
of obstructions. Remove all rubbish such as packing
materials, as soon as the installation is completed.
• Regularly clean the exposed pipework to remove all dust
and dirt. This makes detection of water leaks easier, and
they can be repaired before more serious faults develop.
• Confirm that all screwed and bolted connections and
joints are secure. Secure connections prevent leaks and
vibration from developing.
• Check that all insulation joints are securely closed and that
all insulation is firmly in place. Check all heat exchangers
and all pipework.
• Confirm regularly that any phase imbalance in the three-
phase power supply is within acceptable limits.
• Lubricate the hinges, locks and latches on the electrical
control box doors sparingly.
Liquid refrigerant charging
Checking the charge
WARNING: When adjusting the refrigerant charge always
ensure that water is circulating in the evaporator in order to
prevent any possibility of freezing up. Damage caused by
freezing is not covered by the product warranty.
30GH and 30GZ units are shipped with a full normal charge of
refrigerant. Refer to the Physical Data table. If it is nevertheless
necessary to add more refrigerant, run the unit at full capacity
for some time and then add refrigerant until there are no
bubbles in the sight glass. This will generally mean adding
more refrigerant than would be needed to prevent bubbles from
being seen in the sight glass.
Positive pressure shows that refrigerant is present. If there is no
refrigerant vapour pressure, the whole circuit must be checked
for leaks. When all leaks have been repaired, the entire circuit
must be pumped out and evacuated before being recharged
with clean refrigerant.
Refer to the Standard Service Techniques, Chapter 1, which
describes leak testing methods and pumping down and
evacuation procedures.
Liquid refrigerant charging is recommended as the method to
be used when adding a supplementary refrigerant charge. Charge
through the 1/4" flare connection on the liquid line stop valve.
Never add liquid refrigerant through the low pressure side of
the circuit.
WARNING: To ensure proper operation of 30GH and 30GZ
units there must be at least 5 K liquid subcooling at the inlet to
the expansion valve.
The 30GH and 30GZ units use halocarbon refrigerant. For
your information, we are reproducing here some extracts from
the official publication dealing with the design, installation, oper-
ation and maintenance of air conditioning and refrigeration
systems and the training of people involved in these activities,
agreed by the air conditioning and refrigeration industry.
Refrigerant guidelines
Refrigeration installations must be inspected and maintained
regularly and rigorously by specialists. Their activities must be
overseen and checked by properly trained people. To minimise
discharge to the atmosphere, refrigerants and lubricating oil
must be transferred using methods which reduce leaks and
losses to a minimum.
• Leaks must be repaired immediately
• A valve on the condenser liquid refrigerant outlet line
enables the refrigerant charge to be transferred to the
receiver provided specifically for this purpose.
• If the residual pressure is too low to make the transfer
alone, a purpose-built refrigerant recovery unit must be
used.
• Compressor lubricating oil contains refrigerant. Any oil
drained from a system during maintenance must therefore
be handled and stored accordingly.
• Refrigerant under pressure must never be discharged to
the atmosphere.
Recharging liquid refrigerant
CAUTION: 30GZ 009-035 units are charged with liquid
HFC-407C refrigerant.
This non-azeotropic refrigerant blend consists of 23% R-32,
25% of R-125 and 52% R-134a, and is characterised by the fact
that at the time of the change in state the temperature of the
liquid/vapour mixture is not constant, as with azeotropic
refrigerants. All checks must be pressure tests, and the
appropriate pressure/temperature ratio table must be used for
the interpretation of the values.
Leak detection is especially important for units charged with
refrigerant R-407C. Depending on whether the leak occurs in
the liquid or in the vapour phase, the proportion of the different
components in the remaining liquid is not the same.
NOTE: Regularly carry out leak checks and immediately repair
any leak found.
Undercharge
If there is not enough refrigerant in the system, this is indicated
by gas bubbles in the moisture sight glass. There are two
possiblities:
• Small undercharge (bubbles in the sight glass, no
significant change in suction pressure).
- After detection and repair the unit can be recharged.
- The replenishment of the charge must always be done
in the liquid phase at the liquid line. The refrigerant
cylinder must contain a minimum of 10% of its initial
charge.